1. Field of the Invention
This invention relates to a coupling device allowing fluid to flow from one pipe to another pipe. More particularly, it is concerned with a coupling device providing electrical and thermal insulation under high-pressure, cryogenic conditions for silicon wafer processing.
2. Description of the Prior Art
The process of etching in a single-wafer reactor is a rapidly advancing art. Increasingly, process requirements dictate that some etching be done under cryogenic conditions. That is to say, that the silicon wafer, and the chuck the wafer is mounted on, be at cryogenic temperatures during the etching of the wafer. In some applications, helium gas under high pressure is the most suitable agent for cryogenic cooling. In other words, a high-pressure refrigeration system must be coupled with a single-wafer reactor in some circumstances. In order to effectively couple the refrigeration system with the reactor, a coupling device which insures adequate insulation and sealing at high pressure and low temperature must be provided.
In the prior art sealing under cryogenic temperature and sealing under high pressure have been separately addressed by various solutions. For example, under conditions of cryogenic temperature, two metal conduits coupled by an intermediate ceramic piece have been used. The ceramic interface with either conduit has been fused with the use of a very thin metal joint, for example, a joint made of a nickel/iron alloy. This type of structure works well at cryogenic temperatures, but when such a device is subjected to high pressures the thin metal joint gives way and is disadvantageously deformed causing undesirable leakage of the fluid. This device may not be adapted by thickening the metal seal because to do so would destroy the efficacy of the device under cryogenic temperatures. In other words, it is the thin configuration of the metal seal which allows it to contact beneficially under the cryogenic conditions.
Under high-pressure conditions synthetic-resin seals, such as "TEFLON" O-rings, have often been used successfully. Synthetic-resin seals (without any kind of metal reinforcement), however, tend to fail at cryogenic temperatures.
Additionally, while a synthetic resin such as "TEFLON" works adequately well in sealing with ceramic under high-pressure conditions, an additional problem with metal seals, e.g. copper seals, is that there is a tendency to damage the ceramic portion of the interface because the metal is so much harder and the ceramic is relatively incompressible and brittle compared to the metal.
Thus there is a need for a device which provides electrical and thermal insulation between metal conduits while providing adequate sealing under high-pressure, cryogenic conditions.